Study of electronic states of surface material by using variable temperature scanning tunneling microscopy

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Tunneling spectoscopy by a scanning tunneling microscope (STM) is used as a unique method for studying local electronic states at surfaces with atomic resolution. The aims of this project are to apply this method to the study of electronic states of materials at surfaces and to clarify the relation between the observed phenomena and the electronic states. For these purposes, we have imporoved our STM's to have the functions for spectoscopy and to operate at various temperature.In the instrumentations, we made surface cleaning and evaluation apparatuses together with those for foreign species on the surfaces. By transferring these sampoles to the STM,we can measure the structure of the surfaces and local tunneling spectra.Using an STM operating very low temperature, we studied ;1.search for superconductivity and magnetic flux at Ag/Ge (001) surfaces,2.new charge density wave (CDW) at 2H-NbSe_2 surfaces, and proximity of superconductivity to the CDW state,3.local breaking of superconductivity by magnetic small particles on the 2H-NbSe_2 surfaces.We measured electronic density of states around the Fermi level by tunneling spectoscopy between 2 K and 10 K,and clarified the dependence on the surface structure and temperature.At room temperature, we studied ;1.laser-induced molecular desorption from chlorine or hydrogen adsorbed Si surfaces,2.hydrogen and chlorine exchange reaction at Si surfaces,3.atomic structure of Ag adsorved Ge surfaces,4.visible and infra red light induced local tunneling current at Si surfaces.We observed STM images at various sample bias voltages on the surfaces, and clarified desorption sites and reaction sites, structures of small AG/Ge surface alloy, and the origin of light induced current with atomic resolution.